PROJECT SUMMARY Heart Failure (HF) in the United States alone affects approximately 5.7 million individuals. It is a costly, debilitating and deadly disease with nearly 50% mortality rate within 5 years of diagnosis. More than one-half of all HF patients are diagnosed with HF with preserved ejection fraction (HFpEF, also known as diastolic heart failure) for which there is no effective treatment. Our goal is to investigate the unique role of coronary microvascular dysfunction (CMD) in the development of HFpEF, and to identify novel targets in coronary microvessels for pharmacological prevention of left ventricle (LV) diastolic dysfunction. Our preliminary data reveals a novel mechanistic link between CMD and LV diastolic dysfunction in HFpEF. In patients with HFpEF and multiple rodent models of HFpEF (obese ZSF1 rats and obese db/db mice) we identify a critical deficit in conducted vasodilation, which normally coordinates upstream coronary arteriole dilator signaling to efficiently couple myocardial perfusion with metabolic demand. We further identify a greater expression of adenosine kinase (ADK) in the vascular endothelial cells (EC) in both patients and animals with HFpEF. We hypothesize that ADK inhibition augments endogenous adenosine (ADO) levels to amplify conducted vasodilation and thereby improve LV diastolic function in HFpEF. We will test our hypothesis through pursuing the following Specific Aims: Aim 1: Define the mechanisms of impaired conducted vasodilation in HFpEF. Using ex vivo coronary arteriole preparations from a rat HFpEF model, the obese ZSF-1 vs. lean control rats, we will measure conducted vasodilation and test if impaired gap junction coupling and EC Ca2+-induced hyperpolarization spread is mediated by TNF-induced upregulation of ADK, which diminishes ADO effects in coronary arterioles in HFpEF. Aim 2: Determine the mechanisms by which inhibition of ADK improves LV diastolic dysfunction in HFpEF. Using non-invasive echocardiography and invasive pressure-volume relationship measurements, as well as ex vivo Langendorff-perfused hearts and in vitro EC culture we will determine if pharmacological ADK inhibition in the ZSF-1 rats or EC-specific genetic deletion of ADK in the obese, db/db mice improves LV perfusion and LV diastolic function. We will test if ADK inhibition augments conducted vasodilation and activates eNOS, which increases endogenous NO production to improve LV perfusion and LV diastolic dysfunction in HFpEF. Proposed studies outline a novel therapeutic approach to augment vascular ADO levels by ADK inhibition and thereby stimulate endogenous NO production at the right place and time to ameliorate LV diastolic dysfunction in HFpEF.